weather vane

noun3

1. •
   A mechanical device rotating around one axis and attached to an elevated object such as a roof for showing the direction of the wind.

   • From the graveyard gate one can count a dozen gayly painted farmhouses; the gilded weather-vanes on the big red barns wink at each other across the green and brown and yellow fields. — 1913
2. •
   (figurative) A person or organization that changes their attitude and position based on the prevailing conditions rather than displaying any conviction.

   • The man who changes with every wind of doctrine is not a thinker but a weather vane. — 1960
3. •
   An indicator; something that reflects what the current situation is.

   • Possibly though the best weather vane of the shippers' condition is the attitude of the mill trade as a whole toward present laxness in new orders. — 1918